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Chemical Formula | CaMgSi2O6 |
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Composition | Calcium magnesium silicate, often with some iron |
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Variable Formula | Ca(Mg,Fe)Si2O6 |
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Color | Light green, dark green, gray, light blue, purple, white, colorless |
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Streak | Light green, light gray, white |
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Hardness | 5 - 6 |
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Crystal Forms and Aggregates |
(Monoclinic) Usually as single, short prismatic crystals. Crystals may also be somewhat elongated, and usually have good terminations. Also occurs massive, grainy, columnar, bladed, fibrous, as cleavage fragments, and in disordered aggregates of elongated crystals. |
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Transparency | Transparent to translucent |
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Specific Gravity | 3.3 - 3.6 |
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Luster | Vitreous, dull |
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Cleavage | 1,2 - prismatic at cleavage angles of 87º
and 93º (characteristic of minerals in the pyroxene group). May also exhibit parting in one direction. |
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Fracture | Uneven |
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Tenacity | Brittle |
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Other ID Marks | Some specimens, usually only white "Malacolite" (see below in varieties) fluoresce |
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Varieties |  Chrome-diopside -
Emerald-green, chromium-rich variety Violane
- Light blue to purple, manganese-rich variety Malacolite
- White or lightly tinted, fluorescent variety Salaite
- Diopside with a large iron content Dekalbite
- Diopside free of iron impurities |
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In Group | Silicates ; Inosilicates ; Pyroxene group |
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All About | Diopside forms a series with Hedenbergite (CaFeSi2O6), and may be partially replaced by it. Diopside almost always contains a slight amount of iron replacement. Pure, iron-free Diopside is rather uncommon. |
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Uses | Diopside creates fine collector specimens, and examples from famous localities are highly priced. Diopside is faceted into gems for collectors, although the emerald-green, chromium-rich variety is slowly seeping into the real gem market. Some polished specimens display asterism. |
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Striking Features | Color, cleavage angles, and localities |
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Popularity (1-4) | 2 |
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Prevalence (1-3) | 1 |
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Demand (1-3) | 1 |
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Distinguishing Similar Minerals |
Epidote - different
cleavage, usually darker green, usually heavily striated Enstatite - very difficult to distinguish Augite - very difficult to distinguish Olivine - different cleavage, occurs in different environments Hedenbergite - usually darker in color |
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Commonly Occurs With |
Grossular, Vesuvianite, Dolomite, Actinolite, Tremolite, Andradite, Wollastonite, Phlogopite, Serpentine, Chlorite, Fluorite, Chondrodite |
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Noteworthy Localities |
Diopside is a common mineral and is found
worldwide. However, well crystallized or transparent
specimens come from only a limited number of localities.
Only the finest are mentioned: Some of the best specimens came from Italy. Localities there include Val d'Fassa (Fassa Valley), Trento; Mt. Vesuvius; Val d'Ala (Ala Valley), Piedmont; and Val d'Ossola (Ossola Valley). Other well known occurrences are Binntal, Switzerland; Zillertal, Austria; and Lake Baikal, Russia. In Canada, fibrous bundles occur with green Grossular in Brompton Lake Quebec. Other famous localities in Quebec are Oxford, Sherbrooke Co., and the Jefferey Mine, Asbestos. Diopside also occurs in Ontario in Cardiff, Haliburton Co. The finest U.S. occurrence is DeKalb, St. Lawrence county, New York, where totally transparent, light green crystals were found. New occurences of darker colored material were recently discovered in areas nearby. Specimens also come from Sanford, York Co., Maine and the Crestmore Quarry, Riverside Co., California. A white to creamy-yellow variety fluorescing bluish-white is found in Pawling, Dutchess Co., New York. The variety Violane comes from Saint Marcel, Italy, and Chrome-diopside from Outokumpu, Finland; Mt. Vesuvius, Italy; and the Ural Mountains of Russia. |
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